The present invention relates to a semiconductor processing system used for producing VLSIs, ICs, and the like.
It is well known that the dust is serious bar to the fabrication processes of semiconductor devices such as ICs especially in the preprocessing step for forming circuit elements on semiconductor wafers and in the transferring step of wafers between processing equipments. Cleanliness in a working atmosphere directly determines the product yield.
A SMIF (Standard Mechanical Interface) system (Solid State Technology, July 1984: "SMIF, A Technology for Wafer Cassette Transfer in VLSI Manufacturing", page 111) is known as a conventional semiconductor processing system which satisfies such a processing condition of semiconductor devices.
As shown in FIGS. 1 and 2, the SMIF system consists of a semiconductor wafer cassette 6 for housing a predetermined number of semiconductor wafers 7, a SMIF pod 8 for enclosing the semiconductor wafer cassette 6 airtightly and for transferring the semiconductor wafers 7 in the cassette 6 without exposing them to outside contamination, a wafer processing equipment 1 for processing the semiconductor wafers 7, and a pair of SMIF arms 4 and 4 provided on both sides of the processing equipment 1 for loading and unloading the cassette 6 to and from the processing equipment 1. The SMIF pod 8 consists of a box-like pod body with an open bottom and a bottom plate 10 for closing the bottom of the pod body 9. The bottom plate 10 is detachably attached to the pod body 9 by latches (not shown) provided on the pod body 9 and is arranged to support the cassette 6 at a proper position when the cassette 6 is enclosed in the pod 8. The bottom plate 10 of the SMIF pod 8 is fixed to the pod body 9 while the pod 8 is transported by a worker or a conveying apparatus. As shown in FIG. 1, the wafer processing equipment 1 consists of an equipment body 2 having a first port for the cassette 6, a transparent canopy 5 for covering an upper surface of the equipment body 2, and a clean air supply unit 3 mounted on the canopy 5. This clean air supply unit 3 having a high-performance filter and a blower supplies the wafer processing equipment 1 with clean air.
In order to transfer the cassette 6 into the processing equipment 1, the cassette 6 enclosed in the SMIF pod 8 is placed on the upper face of one of the SMIF arms 4. When the pod 8 is placed on it, the bottom plate 10 of the pod 8 is detached from the pod body 9, and then the bottom plate 10 and the cassette 6 supported on it are loaded into the SMIF arm 4. Thereafter, only the cassette 6 is transferred into the processing equipment 1, set in the first port, and then the wafers 7 in it are withdrawn to be processed.
After being processed in the processing equipment 1, the wafers 7 are housed in another cassette (not shown) and are loaded in the other SMIF arm 4. In this arm 4, the cassette is brought into another SMIF pod (not shown) which has been placed on the upper face of the other SMIF arm 4 without being exposed to outside contamination. After that, the pod 8 which has just received the cassette is transported, for example, by a worker to another processing equipment (not shown) of the next fabrication process and then placed on an SMIF arm of this equipment. Thereafter, the wafers 7 are processed in the equipment in the same manner as described above.
Accordingly, the wafers are not exposed to outside contamination but kept in clean air while being transported by workers and being transferred between the pod 8 and the equipment 1 as well as while being processed in the processing equipment. Therefore, a high product yield is maintained by using this SMIF system even when cleanliness (based on U.S. Federal Standard No. 209b) of a clean room in which the system is installed is about class 1,000 to 100,000. As a result, a non-laminar flow air current system which keeps its environment at cleanliness of class 1,000 to 100,000 is possibly employed in the clean room in place of a laminar flow air current system which keeps its environment at ultra high cleanliness of class 10 to 100. That is, associated facilities of the clean room become simple, and costs for its construction, facilities, and maintenances can be greatly reduced. Furthermore, it is not necessary, if the SMIF system is used, to limit the behaviour of workers who works in the clean room as strictly as it is limited in a clean room with ultra high cleanliness of class 10 to 100. The workers are allowed to work as if they are in an ordinary room on condition that they will wear simple clean room clothes. They are able to work more comfortably in this clean room using the SMIF system than in one not using it.
However, in the conventional semiconductor processing system described above, an installation space for the system including spaces for the two SMIF arms is required in a clean room, since the SMIF arms 4 must be attached on both sides of the wafer processing equipment 1. As a result, the conventional system not only makes it difficult to effectively utilize a floor space in the clean room, but also makes its total cost quite high.